炭包覆纳米硅复合负极材料的制备及其性能研究

发布时间：2018-01-15 03:28

本文关键词：炭包覆纳米硅复合负极材料的制备及其性能研究　出处：《中国林业科学研究院》2017年硕士论文　论文类型：学位论文

【摘要】：锂离子电池的能量密度高,无记忆效应,循环稳定性好,对环境无污染,且安全系数较高,故在众多的储能装置中出类拔萃,得到广泛关注。但随着科学技术的进步,各类电子设备、电动仪器、军事装备等对电极材料的要求越来越苛刻,只有开发出高容量、高稳定性的大功率锂离子电池才能满足社会发展的需要。负极材料至关重要,硅作为能量密度高的新型负极材料,成为研究者关注的焦点。但硅在电池循环过程中体积会发生严重的膨胀,导致电池容量锐减,阻碍了硅负极的商业化,但炭材料的存在可以弥补这一缺陷,炭材料嵌锂电位较低,在电池充放电循环过程中容量不会骤减,稳定性好,且体积变化不明显,若将硅与炭材料复合,则可以最大限度的发挥两者的优势,有望制备出比较理想的负极材料。本研究以乙基纤维素为碳源,经水热碳化及高温炭化、HF刻蚀SiO2后制备了炭包覆纳米硅复合负极材料,并将其组装成扣式电池。考察了反应条件对微球制备的影响,探讨了高温炭化温度、硅含量对负极材料电化学性能的影响。并利用SEM、XPS、FT-IR、XRD、激光粒度分析等对材料的形貌、粒径分布、官能团分布、晶体结构等进行表征,SEM及激光粒度分析显示微球的球型较好,平均粒径为7.2μm;FT-IR及XPS结果显示,在水热碳化过程中产生了芳环及羧基结构;此外,XRD谱图上可以明显看到硅及无定形碳的吸收峰;恒电流充放电及倍率性能测试显示,在首次充放电循环中,材料的放电比容量为930.3 mAh/g,相应的库伦效率为69.1%,当循环至第40次时,电池的容量保持率为64.7%。以丙烯酰胺为单体经反相悬浮聚合得到聚丙烯酰胺,并以其为氮源、碳源,经高温炭化及HF刻蚀SiO2后制备了氮掺杂炭包覆纳米硅负极材料,并将其组装成扣式电池。研究了原料用量及剪切速度等对微球制备的影响。SEM及激光粒度分析表明微球顺滑圆整,平均粒径为10.1μm;FT-IR显示丙烯酰胺很容易聚合为聚丙烯酰胺,XRD显示氮掺杂炭材料包覆纳米硅未改变其晶体结构。电化学性能测试表明在第一圈充放电循环中,复合材料的放电比容量为1 055.5mAh/g,相对应的库伦效率为71.8%,倍率性能测试结果表明由于氮元素的掺杂负极材料在大电流密度下的容量衰减减缓,稳定性提高。
[Abstract]:Li-ion battery has high energy density, no memory effect, good cycle stability, no pollution to the environment, and high safety factor, so it is outstanding in many energy storage devices. But with the progress of science and technology, all kinds of electronic equipment, electric instruments, military equipment and other electrode materials are increasingly demanding, only to develop high capacity. High-stability high-power lithium ion batteries can meet the needs of social development. Negative electrode material is very important. Silicon is a new type of negative electrode material with high energy density. However, the volume of silicon in the battery cycle will be seriously expanded, resulting in a sharp reduction in the capacity of the battery, which hinders the commercialization of silicon negative electrode, but the presence of carbon materials can make up for this defect. The lithium intercalation potential of carbon material is low, the capacity will not be reduced, the stability is good, and the volume change is not obvious during the battery charge and discharge cycle, if the silicon and carbon materials are combined, the advantages of the two materials can be maximized. In this study, carbon coated nano-silicon composite anode material was prepared by hydrothermal carbonization and high temperature carbonization HF etching SiO2 with ethylcellulose as carbon source. The effect of reaction conditions on the preparation of microspheres was investigated. The effects of high temperature carbonization temperature and silicon content on the electrochemical properties of negative electrode materials were investigated. The morphology, particle size distribution, functional group distribution and crystal structure of the materials were characterized by FT-IRN XRD and laser particle size analysis. The results of SEM and laser particle size analysis showed that the spherical shape of the microspheres was better. The average particle size was 7.2 渭 m; The results of FT-IR and XPS showed that aryl rings and carboxyl groups were formed during hydrothermal carbonization. In addition, the absorption peaks of silicon and amorphous carbon can be clearly seen on the XRD spectra. The constant current charge-discharge and rate performance tests show that the discharge specific capacity of the material is 930.3 mg / g and the corresponding Coulomb efficiency is 69.1% in the first charge-discharge cycle. At the 40th cycle, the capacity retention rate of the battery was 64.7. Polyacrylamide was synthesized by reverse suspension polymerization with acrylamide as monomer, and it was used as nitrogen source and carbon source. After high temperature carbonization and HF etching of SiO2, nitrogen-doped carbon coated nanocrystalline silicon anode materials were prepared. The effects of the amount of raw materials and shear rate on the preparation of microspheres were studied. SEM and laser particle size analysis showed that the microspheres were smooth and round with an average diameter of 10.1 渭 m. FT-IR showed that acrylamide was easily polymerized into polyacrylamide. The results showed that nitrogen-doped carbon coated with nano-silicon did not change its crystal structure. The electrochemical performance test showed that in the first cycle of charge and discharge. The specific discharge capacity of the composite is 1 055.5 mg / g, and the corresponding Coulomb efficiency is 71.8%. The results of the rate performance test show that the capacity attenuation of nitrogen-doped anode materials at high current density is reduced and the stability is improved.
【学位授予单位】：中国林业科学研究院
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TM912

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